Edit your account password and edit your email preferences for having the site notify you about PMs (in the 'Account' tab)

At login, If you selected the option to 'remember to keep me logged in', that's called a 'persistent login'. You can then clear all and any persistent logins you may have in the 'Profile' tab. If you clear out persistent logins, your current session will stay open but, next time you visit the site, you will need to login.

That's a quick run down of some of the key features in your 'My Account' section of the site.